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Discussion Starter · #1 ·
A little background. 83 F150 4wd 302 carb'd. Original motor threw a rod, but was running fine before. Found an 86 302 out of a Mustang. Swapped motors, used our intake and dizzy because it didn't have one.
Put #1 at TDC on Compression stroke (piston up, timing mark on 0) Correct? Started motor, found some minor vac leaks, and son broke ears off carb where you mount it, changed carb from my other truck that we just drove. Set timing at 9 degrees for now, idles like a new kitten. Firing order is 1-5-4-2-6-3-7-8 checked 3 times. Wires came off other engine and were good.
We still have this pop when the throttle is rev'd. Like I said it idles good and you can rev it slowly.
1. Checked compression, 172 on the highest and 164 on the lowest cylinder.
2. Pulled off intake and changed gaskets, pulled off carb and changed gaskets.
3. Vac advance works and we have 36 degrees total advance.
4. Carb worked good on other truck ( drove truck and switched carb same day)
5. New wires, rotor, cap and plugs.
6. Plugged all vac lines except for the brake booster. Brakes seem to work fine, no constant hissing when you hold them.
7. Changed fuel pump and took off fuel filter.
8. Put linkage to accel. pump in every available spot.
9. Pulled hair out and cursed truck. Threatened to burn truck to the ground.
10. Shopped e-bay for large stick of dynamite.
11. Swapped firing order and truck wouldn't even start.
I know I am forgetting something we did. It is only 1 big pop through carb when throttle is hit fast. Help !!!!!!!
 

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You have narrowed down alot of possibilities. My initial guess is to check and see if the timing chain is stretched. Try roatating the motor back and forth at the damper and seeing how far you can rotate the engine before the rotor spins.
if it seems excessive, then you may want to take off the front cover and varify to timing chain is not stretched.

It the only thing I can think of right now that you have not checked.
 

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To help with your first question on TDC. Just because your timing mark is at 0 doesn't mean you are on the compression stroke. This is because the camshaft makes 2 revolutions for every turn of the crank, and the timing marks are on the crank. So at the 0 degree mark, you can still be 180 degrees off. The best way to ensure TDC on the compression stroke is to pull the valve cover and make sure you are coming up to TDC after the intake valve has closed. Another way is to hold your thumb over the spark plug hole and feel for compression.

However, since you have checked the timing with the engine running (i assume), this is a non-issue.

Are you sure that is the firing order for the new engine you dropped in? the camshaft is what controls the firing order. They have a different firing order depending on if they are H.O. or non H.O. The engine will actually run if you switch these up, but will cause backfiring through the carb.

I believe this is right but I don't have a manual for the mustang:

non-H.O. is 1-5-4-2-6-3-7-8
and the H.O. is 1-3-7-2-6-5-4-8

make sure you are going counter-clockwise around the distributer when you hook up the wires

#1 cyclinder is the front (toward front of vehicle) passenger side going to the rear of the passenger side to #4, then back to front drivers side for #5 then to the rear of the drivers side for #8

I would dbl check this with the correct manual though
 

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Discussion Starter · #4 ·
Set timing at 4,6,8,10 degrees still pops. Changed firing order to 1-3-7-2-6-5-4-8 and it barely runs, so firing order is correct. Will check for timing chain slack today. Any way I can check the cam easily? One more thing, we took off the EGR spacer under the carb and replaced it with a phenolic spacer, could this be our whole problem? We even set timing for max vac. and it still does it. I am wondering about the EGR plate or spacer, whatever you call it.
 

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Discussion Starter · #10 ·
Billz4x4z said:
No,you don'y want manifold vacum.
Try a port off the carb that gets vacum as you snap the throttle open.
If I am adjusting for most vacum at idle and there is no vacum at the carb port until I snap the throttle how do adjust the carb. Not being smart, but do I hold the gas open a little or are you talking about a carb port that has vac at idle and not to use a manifold port. I need all the help I can get on this one.
 

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You want a carb port that has no vacum at idle,but as you apply throttle you get vacum.Easy way to do it is throw your vacum gauge on a port that appears to have no vacum at idle,snap the throttle and if you get vacum thats the port you want your vacum advance on.When balancing the carb,manifold vacum,or constant vacum source is needed.
 

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Discussion Starter · #12 ·
Update, Rebuilt extra carb I had and also installed the EGR plate and new gaskets. Still have popping through the carb and seem to have a worse vac leak. Only getting 15 on the vac gauge had 18 before and the idle screws barely make a difference when adjusted, been real busy lately so am trying to play with it a little at a time. Also, I have the brake booster hooked to the T off the manifold, EGR hooked to same T, PCV is going into big port on carb, Vac advance hooked to passenger side front port on carb and that is all, does this sound correct? Get max vac with the timing set between 7 and 9 degrees, also seems to idle smooth at that setting. Will look for vac leak before I continue looking deeper.
 

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Discussion Starter · #13 ·
Plugged all vac lines and it still pops. Adjusted timing and carb and finally got 18 on the vac gauge. Pops still. Decided to double check vac advance and danged if it isn't working, can't get a vac at all on the thing, must be a bad diaphragm. Will change that today, I still think it shouldn't pop even without it hooked up, but have never tried before on another motor. If this doesn't work I'm wondering if the carb is big enough, I don't know the full history of this motor so it may have been gone through and bored out, heads may have been done also so I'm not for sure.
 

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mchipman said:
Plugged all vac lines and it still pops. Adjusted timing and carb and finally got 18 on the vac gauge. Pops still. Decided to double check vac advance and danged if it isn't working, can't get a vac at all on the thing, must be a bad diaphragm. Will change that today, I still think it shouldn't pop even without it hooked up, but have never tried before on another motor. If this doesn't work I'm wondering if the carb is big enough, I don't know the full history of this motor so it may have been gone through and bored out, heads may have been done also so I'm not for sure.
Looks like your on the right track,Get the advance working and go from there.
 

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Discussion Starter · #15 ·
Another update in the carb saga. See if I did this correctly. Wanted to check firing order, this is what we did. Changed advance no help.

1. Set #1 at TDC (0 on balancer, piston at top, felt compression, rotor pointing at #1 on dizzy)
2. Turned motor until the next cylinder came on compression stroke, turned out to be the #3 ( balancer turned about 120 degrees)
3. Continued, #7 was next and then #2.
It seems we were using the wrong order as everyone has suggested, the problem is, we changed order to 1-3-7-2-6-5-4-8, now it won't start at all.
When timing is retarded it backfires through the exhaust and when it is advanced as far as the dizzy will let me it tries but won't start.
Will pull dizzy out tonight and rotate advanced 1 tooth. Does anyone have an easy way to line up the oil pump shaft?
Does all this sound right for the problem we are having?
Carb is a stock Motocraft 2 BBl
If this fails I will pull of valve covers.
 

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Discussion Starter · #16 ·
Update, I hate when people don't post when things are fixed, FrankenTruck lives. After re-doing the firing order and a vac leak and moving the dizzy 2 teeth it runs and drives fine. Some minor tuning but it is good, thanks to all that helped.
 
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